Apparatus for controlling rolling mill

ABSTRACT

A system for controlling rolling mills, especially roll contour, has hydraulic motors supplied with working fluid through a pressure regulator. The downstream pressure of the working fluid from the pressure regulator is adjusted by selectively supplying and venting fluid from a loading chamber of the pressure regulator. The loading and unloading controls are of a nature that permits remote location, and they are operated by an attendant in accordance with signals from the mill indicating errors in the dimensions of metal being rolled by the mill. Automatic operation can be substituted for the manual operation and programmed control of the pressure can also be used. Loading and unloading valves have actuators providing dither for the valve to prevent the difference in flow rates when flow is increasing as compared to conditions when flow is decreasing.

etry et all.

APPARATUS TU "CUNTUILTJING UTJLTNG MllTslls lllenry ATred lPetry,Sparta; Francis Rerecicli, Dover; Gerhard Spangenlberg, Boonton, all ofNJ.

Assignee: Mlnrottn Valve Corporation, Boonton, NJ.

Filed: June 16, 1969 Appl. No: 033,286

Inventors:

US. Cl ..72/16, 72/28, 72/245 lint. Cl. ..]Hl2lllr 37/02, B21b 37/06,B2lb 31/32 lFielld at Search ..72/8, 9, 16, 28, 246, 245,

References Cited UNlT ED STATES PATENTS 3,024,679 3/1962 Fox ..72/245Primary Examiner-Milton S. Mehr Attorney-Sandoe, Hopgood & Calimafde [57] ABSTRACT A system for controlling rolling mills, especially rollcontour, has hydraulic motors supplied with working fluid through apressure regulator. The downstream pressure of the working fluid fromthe pressure regulator is adjusted by selectively supplying and ventingfluid from a loading chamber of the pressure regulator. The loading andunloading controls are of a nature that permits remote location, andthey are operated by an attendant in accordance with signals from themill indicating errors in the dimensions of metal being rolled by themill. Automatic operation can be substituted for the manual operationand programmed control of the pressure can also be used. Loading andunloading valves have actuators providing dither for the valve toprevent the difference in flow rates when flow is increasing as comparedto conditions when flow is decreasmg.

7 lawn 1111 Drawing Patented March 14, 1972 7 3,648,496

3 Sheets-Sheet 1 GAUGE INVENTORS ATTORNEYS.

APPARATUS FOR CONTROLLING ROLLING MILL BACKGROUND AND SUMMARY OF THEINVENTION One of the problems encountered in rolling mills involvesvariations in the dimensions of the work piece along its length andtransverse of its width. Particularly with mills for rolling sheetmetal, the gauge of the metal is often greater toward the center of thestrip than near the edges.

Efforts have been made to overcome this variation in gauge by providingthe work rolls of the mill with a crown and applying pressure to theaxles of the work rolls to change the contour of the rolls by bendingthem slightly to compensate any errors in gauge during a rollingoperation.

This invention combines with the pressure-applying apparatus of the workrolls an improved system for applying pressure to change the contour ofthe work rolls. In its broadest aspects, the invention provides animproved system for applying constant pressure to an element and assuresthe degree of pressure necessary in response to error signals from thework to which the pressure is applied.

In the case of rolling mills, the invention supplies working fluid tothe motors or other means that exert the pressure which is to becontrolled; this pressure being applied to the axles of the work rollsof the mill to bend the rolls with a maximum diameter crown as thecenter fulcrum. The working fluid for the motors is supplied by apressure regulator having a chamber that is subject to the pressure ofthe working fluid supply to the motors, i.e., the downstream pressure ofthe regulator, and this pressure acts against a movable wall of theregulator having a loading chamber on its other side.

The loading chamber is loaded and unloaded by valve means that supplythe same kind of working fluid to the loading chamber as is controlledby the main valve of the regulator in the preferred construction.

The valves that supply the fluid to the loading chamber have actuatorsthat provide dither to the valves to reduce static friction so that thefluid flow for a particular valve operating force is substantially thesame whether the valve is moving toward open or closed position.

In the preferred embodiment, the invention has separate operating meansfor different sides of the mill and this provides greater flexibility ofadjustment to correct errors in gauge that may not be symmetrical aboutthe center line of the strip or other work piece; and the rate ofcorrection is responsive to the extent of displacement of the controls.

Other objects, features and advantages of the invention will appear orbe pointed out as the description proceeds.

BRIEF DESCRIPTION OF DRAWING In the drawing, forming a part hereof, inwhich like reference characters indicate corresponding parts in all theviews:

FIG. I is a diagrammatic view of a rolling mill equipped with rollpressure controls made in accordance with this invention;

FIG. 2 is an enlarged diagrammatic view of one of the roll passes ofFIG. I;

FIG. 3 is a diagrammatic wiring and piping diagram for the rolling millcontrol shown in FIG. 1',

FIG. 4 is a schematic view showing the correlation of the control valvesfor the system shown in FIG. 3;

FIG. 5 is a greatly enlarged sectional view through one of theregulators shown in FIG. 3;

FIG. 5a is an enlarged, fragmentary view of the main valve element shownin FIG. 5;

FIG. 6 is a fragmentary and partly diagrammatic end view of theregulator shown in FIG. 5;

FIG. 7 is a wiring diagram for the control connections showndiagrammatically in FIG. 3;

FIG. 8 is a graph showing the principle of operation of the electricalcontrols shown in FIG. 7;

FIG. 9 is a chart showing the effect of friction on the operation of thepilot valves and the resulting fluid flow; and

FIG. 10 is a chart similar to FIG. 9 but showing the improved resultsobtained when the control means provides dither for the pilot valves.

DESCRIPTION OF PREFERRED EMBODIMENT FIG. I shows a rolling mill havingsuccessive roll stands I6 and 118 through which a metal strip 20 passes.Each of the roll stands 16 and 18 is a four-high mill having an upperwork roll 22 and a lower work roll 24. These work rolls 22 and 24 havebackup rolls 26 and 28, respectively.

The roll stands 16 and I8 have long rolls for rolling sheet metal, andthis invention is particularlly concerned with and will be described inconnection with, the control of roll stands for sheet metal. However, inits broader aspects, the strip 20 is representative of metal which isrolled by passing it between work rolls that operate upon the metal tochange its shape or dimensions.

FIG. 2 shows the roll stand 16. The rolls 22 and 24 are crowned and theroll 24 has axle extensions at its opposite ends extending into chocks30 which are movable up and down in a frame 32 of the roll stand inorder to shift the lower roll 24 toward and from the upper roll 22.These chocks 36 are urged upward by cylinder-and-piston motors locatedunder the chocks 30. Each motor includes a piston 34 attached to thechock 3th and a cylinder 36 supported from a lower chock 33 whichprovides a bearing for the backup roll 28.

Working fluid is supplied to the cylinders 36 from a pressure regulatorwhich will be described. The introduction of additional working fluidinto each of the cylinders 36 causes the piston 34 to lift itsassociated chock 38 and this bends the roll 24 about the upper centerregion of the roll 28 where the roll 28 contacts with the work piecewith maximum pressure, this location serving as a fulcrum during thebending of the roll 24.

Both of the hydraulic devices, comprising the pistons 34 and cylinders36, can be operated simultaneously to bend the roll 24 symmetrically, orthe hydraulic devices can be operated separately or with less pressuresupplied by one than the other where the roll is to be bentunsymmetrically because of unsymmetrical errors in the gauge of thestrip passing between the work rolls 22 and 24.

It will be understood that the upper work roll 22 can also be providedwith hydraulic devices for thrusting it toward the lower work roll 24.In some installations the rolls are bent by pushing the crown portion ofthe roll against the backup roll. The rolling mill structure thus fardescribed and illustrated diagrammatically is conventional and thisinvention includes new combinations with a rolling mill of apparatus forcontrolling the operation of the hydraulic devices so as to obtainbetter results, and more especially more unifonn results, in correctingfor errors in the rolling of metal, especially errors in the gauge ofsheet metal. The invention will be described as applied to a single rollstand of a mill; but it will be understood that it can be applied insimilar fashion to any or to all of the roll stands.

FIG. 3 shows the cylinders 36 and pistons 34, and these hydraulicpressure devices are indicated generally in FIG. 3 by the referencecharacters 40. Working fluid passes to and from the respective hydraulicdevices 40 through tubing 42 and 43. The tubing 42 leads to a pressureregulator 46 and the tubing 43 leads to a pressure regulator 48. Thepressure regulator 46 and its controls will be described, and it will beunderstood that the pressure regulator 48 and its controls are ofsimilar construction.

In the diagrammatic illustration of FIG. 3, working fluid is withdrawnfrom a reservoir or sump 50 through tubing 52 leading to the inlet sideof a pump 54 driven by a motor 56. The pump 54 supplies pressure throughtubing 58 and 59 leading to the regulators 46 and 48, respectively. Theregulator 46 has a return line 60 consisting of tubing leading back tothe sump 50.

A controller 62 has a handle 64 which moves angularly about an axis intodifferent positions, as indicated by the dotted lines in FIG. 3. Whenthe handle is in the center position, the regulator 46 remains in itslast adjusted position. In order to change the delivery pressure of theregulator 46, the handle 64 is moved to load or unload a loading chamberof the regulator 46. This apparatus will be described in connection withthe other figures, but for the present it is sufficient to understandthat movement of the handle 64 counterclockwise increases the loading ofthe loading chamber of the regulator 46; and movement of the handle 64clockwise from its middle position vents fluid from the loading chamberof the pressure regulator 46.

In the control apparatus shown in FIG. 3 there is another controller 62'having a handle 64 which is operated to control the pressure regulator48 in the same way that the handle 64 controls the pressure regulator46.

These controllers 62 and 62 with their handles 64 and 64 are manuallyoperated controls which are manipulated by an attendant in response tosignal indications from gauge detectors 68 (FIG. 1) located at differentlocations across the width of the strip 20. If one gauge detector showsan increase in the gauge of the strip at the center region and the othergauge detectors indicate that the error is symmetrical, then theattendant operates both of the handles 64 and 64 to cause the hydraulicdevices on the rolling mill to apply additional pressure at both ends ofthe work roll. If the gauge detectors 68 show the error to beunsymmetrical, then the attendant operates only one of the controllers62 or 62' to change the roll contour on whichever side is necessary inorder to minimize the error; or he may operate the controllers 62 and62' in opposite directions so as to increase the pressure at one end ofthe work roll and decrease it at the other, in order to minimize theerror.

The manual controllers 62 and 62' illustrate the invention in itssimplest aspects and it will be understood that the operation can bemade automatic by having the controllers 62 and 62 responsive to signalsfrom the gauge detectors 68; and in more elaborate systems the controlscan be combined with quality control computers which program theoperation and take into consideration other factors such as pressure andtemperature, in addition to the localized gauge readings of thedetectors 68.

FIG. 4 is a schematic showing of the piping connections for controllingthe operation of the pressure regulator 46. The pressure regulator has amain valve element 70 which controls flow of fluid from the inlet tubing58 through the regulator 46 to the outlet tubing 42 which leads to thehydraulic pressure device. The pressure regulator 46 also contains avent valve element 72 which controls the discharge of fluid from theregulator through the return line 60 to the sump 50. This fluid flowingfrom the regulator through the return line 60 may be either fluid ventedfrom the loading chamber of the regulator, or it may be fluid exhaustingfrom the hydraulic pressure device, as will be more fully explained inconnection with FIGS. and 6.

The pressure regulator 46 has the supply of fluid for loading andunloading its chamber controlled by valves 74 and 76, respectively. Thevalve 74 is operated by a solenoid 78 and the valve 76 is operated by asolenoid 80. The energy supplied to the solenoids comes from thecontroller 62; and in the preferred construction, which will bedescribed in connection with FIG. 7, the amount of energy supplied tothe solenoids 78 and 80 depends upon the displacement of the controller62 so that the extent of opening of the valves 74 and 76, and theresultant flow, is proportional to the displacement of the controller62.

When the solenoid 78 is energized, fluid flows from the inlet tubing 58through a passage 82 in the regulator body, and past the open valve 74to a passage 84 which leads to the loading chamber of the pressureregulator. When the valve 74 is closed and the valve 76 is open, fluidflows from the loading chamber through a passage 86, past the open valve76, and through a passage 88 of the regulator to the return line 60.

FIG. 5 shows the internal construction of the regulator 46. The relationof some of the passages is not so clearly shown as in the schematicillustration of FIG. 4 because of the fact that the solenoid-operatedpilot valves 74 and 76 are located in different planes, one behind theother. The inlet tubing 58 connects with an inlet passage 90 which leadsto a main valve chamber 92. The main valve element 70 is located in thisvalve chamber 92 and the portion of the valve chamber 92 beyond the mainvalve element 70 is indicated by the reference character 94. Thisportion 94 of the valve chamber has a passage 96 leading to the outlettubing 42. When the main valve 70 is in open position, fluid flows fromthe inlet 58 through the passage 90 and valve chamber 92 to the passage96 which leads to the outlet tubing 42 that communicates with thehydraulic pressure device.

FIG. 5a shows the construction of the main valve element 70. Itcomprises a stem 98 having a flange with a tapered face 100 behind whichthere is a shoulder 102 against which a plastic facing washer 104 isclamped by a bushing 106, threaded on the stem 98 with a thread lock108, and an O-ring to prevent leakage of pressure behind the facingwasher 104.

When the valve element 70 is in closed position, the facing washer 104contacts with a seat 112 which fits with a press fit into a counterboreand against a shoulder 114 of the counterbore. An O-ring 116 preventsleakage of pressure behind the seat 112.

One end of the valve stem 98 slides in a guide 118 (FIG. 5) in a fitting120 held in a counterbore of the pressure regulator housing by athreaded fitting 122. The end of the guide 118 is closed but the spacewithin the guide communicates with the portion 94 of the valve chamberthrough drilled passages 124 so as to avoid compression of fluid beyondthe left-hand end of the valve stem. A spring 126 urges the main valveelement 70 toward closed position.

The right-hand end of the valve stem 98 slides in a cylindrical guide128 (FIG. 5a). There is a tapered frustoconical face 130 on theright-hand end of the valve stem 98 and this face 130 surrounds a recess132 which communicates through a passage 134 with the portion 94 of themain valve chamber.

A movable element 136 slides in various guides in the housing of theregulator with O-rings to prevent leakage of fluid around the outside ofthe movable element 136. This movable element 136 has a piston portion138 which is a movable wall on the left-hand side of a loading chamber140 of the regulator. The movable element 136 is also an auxiliary valvestem for transmitting motion of the piston portion 138 to the main valveelement 70 when the movable element 136 moves toward the left in FIG. 5.When the movable element moves toward the right, the spring 126 movesthe main valve element 70 into contact with the seat 112.

The movable element 136 also has a plastic valve element 142 thatcontacts with the frustoconical face 130 at the righthand end of thevalve stem 98. This plastic valve element 142 is in closed position incontact with the face 130 whenever the main valve element 70 is open asa result of pressure in the loading chamber 140 holding the pistonportion 138 far enough to the left to open the main valve element.

When the main valve element 70 moves into closed position, any furthermovement of the movable element 136 toward the right causes the plasticvalve element 142 to move away from the frustoconical face 130 and thisshifting of the valve element 142 into open position permits fluid inthe portion 94 of the valve chamber to flow through the passage 134 intothe recess 132, past the valve element 142 into a chamber 144 whichcommunicates with a passage 146 leading to the return line 60. Thus thevalve element 142 serves as a relief valve for pressure in thedownstream portion 94 of the main valve chamber. The movable element 136is moved to the left by pressure in the loading chamber 140 of theregulator, as previously explained; and it is moved toward the right bypressure in another chamber 148 which communicates with the downstreamportion 94 of the main valve chamber through passages 150 and 151. Inthe illustrated construction, the fluid supplied to the loading chamber166 is the same hydraulic fluid as is regulated by the pressureregulator 16 and since this is not a compressible fluid, the loadingchamber of the pressure regulator has to have resilient means formaintaining a load on the substantially incompressible fluid. Thisresilient means includes a stack of Belleville washers 152 held instacked relation by an elastomeric sleeve 15 1 and housed in a cap 156which screws into the end of the regulator along threads 158. Aconventional spring can be substituted for the Belleville washers 152but the washers have the advantage of providing more force and travelwithin a smaller space. The stack of washers 152 contacts with a fitting1611 at one end of the cap 156 and this fitting 161]! extends through anopening 162 in the cap and has an axial opening 161 for free flow of airinto and out ofthe cap 156.

The other end of the stack of washers 152 contacts with a plunger 166which slides as a piston in a cup 1611 threaded into a holder 1711 in acounterbore of the regulator housing.

The space in the holder 1711 between the piston portion 136 of themovable element 136 and the end face of the plunger 166 is the loadingchamber of the regulator. The end of the cup 1611 is open so that thepiston portion 136 confronts the end face of the plunger 166 across theloading chamber. rings 172 prevent leakage of liquid around the outsideof the plunger 166 and cup 169 into the space that holds the stack ofwashers 1152.

As liquid is pumped into the loading chamber 1410, the plunger 166 ismoved to the right in FIG. against the pressure of the washers 152 andthis compression of the washers increases the pressure on the fluid inthe loading chamber and consequently increases the pressure on thepiston portion 138 of the movable element 136. The fluid in the loadingchamber is, in effect, a hydraulic link transmitting pressure of thestack of Belleville washers 152 to the piston portion 136 of the movableelement 136.

The main valve element has the diameter of its contact with its seatcorrelated with the diameters of the portions of the stem that slide inthe guides so that the main valve element is a balanced poppet and itsmovement is subject only to the balance of forces between the spring 126and the downstream fluid pressure in the chamber 149 acting against theannular face of the element 136 which is exposed to fluid pressure inthe chamber 1411], which forces urge the parts toward the right, and thepressure of the fluid in the loading chamber 140 acting against thepiston portion 136 and urging the movable parts toward the left.

The space at the left of the piston portion 1311 is vented to theambient atmosphere through a vent passage 17d, past the end of theholder 1711 and through an opening 175 in the side of the regulatorhousing.

The flow of fluid to and from the loading chamber 140 is through anaxial passage 1811 in the movable element 136 and through a radial bore1132 to a chamber 1134. These passages 11311 and 192 and the chamber 181are portions of the passage 841 from the valve '7 1 to the loadingchamber. The passage 92 that supplies fluid to the valve 7 1 is shown indotted lines in FIG. 5. In practice, it is provided by drillings andcrossdrillings in the block that comprises the housing of the pressureregulator 16; but these drillings and cross-drillings cannot be shown assuch in FlG. 5 and the dotted line for passage 82 is the effectivecourse of the passage.

When the valve 7 1 is in open position, fluid flows from the inlet 90through chamber 92, passage 82, past the open valve 7 1 and throughpassage 8 1 to the loading chamber 1411 re gardless of whether the mainvalve element 711 is open or closed.

The other valve 76 (FlG. t) operated by the solenoid 80 is similar tothe valve 7 which is operated by the solenoid 76. It controls flow offluid from the from the loading pressure chamber through passages 11111,182, and the chamber 184, and through the passage 86 (FIGS. 1 and 6),past the open valve 76 and through the passage 1111 to the return line60. The extent to which valves 741 and 76 are open determines the rateof flow to and from the loading chamber of the regulator and thusdetermines the rate of change of the delivery pressure of the regulator.

FIG 7 shows, diagrammatically, the controller 62. The other controller62 is of similar construction. The handle 641 is secured to a shaft 169.There are two switches 191 and 192 urged into closed positions bysprings 19 1 and actuated into open positions by a plunger 196 for theswitch 191 and by a plunger 197 for the other switch 192. Both of theplungers 196 and 197 bear against a cam 198 on the shaft 196, and thiscam is shaped to let one or the other of the switches 191 and 192 closewhen the cam 199 operates one or the other of the plungers 196 and 197.

Power is supplied to the controller 62 from an alternating current powerline 2011. For some controllers a combination of alternating current anddirect current is used, but the illustrated controller 62 usesalternating current power only. The power passes from a radiofrequencychoke 202 and then through a delaying network 21141 to a solid statetrigger 2116. A solid state switch 266 is provided for the main currentflow.

The delay network 2941 includes an iinductance potentiome ter 210. Abrush 212 wipes along the curved potentiometer to change the inductanceof the circuit of the delaying network. The wiper brush 212 is securedto the shaft 1119 in such position that the wiper is at the midpoint ofthe potentiometer when the handle 641 is in its mid or off positionwhich does not close either of the switches 191 and 192. Changes in thedelaying network change the point in each cycle at which the switch 208closes to supply power to one side of each of the switches 191 and 192.The switch 191 closes to supply power to the solenoid 78 to open thevalve 76 which increases the pressure in the loading chamber of theregulator. The closing of the switch 192 supplies power to the solenoidto open the valve 76 which decreases the pressure in the loading chamberof the regulator.

FIG. 9 shows the principle of operation of the controller shown in FIG.7. With the delaying network adjusted for a long delay, the switch 298(FIG. 7) closes late in the current cycle as indicated by the line 216,and the only power supplied to the solenoid is that represented by thearea under the alternating current curve 218 to the right of line 216.Reducing the delay of the delaying network moves the time of closing ofthe switch forward to the time represented by the line 2211, and thepower represented by the area under the curve 218 to the right of theline 220 is substantially greater than the power to the right ofline216.

The increase in the power supplied to the solenoids increases the pullof each solenoid and increases the extent to which the valve is openedby the solenoid for greater flow of liquid to the loading chamber of theregulator with resulting increase in the rate at which the regulatoradjusts to a higher delivery pressure, or to a lower delivery pressurein the case of the vent valve.

FIG. 8 shows power supplied to the solenoids for both the plus and minushalves of the alternating current wave. In prac' tice, this power can berectified at the solenoid either by half wave or full waverectification. One of the advantages of the pulse power supply to thesolenoids is that the pulsing force applied to the valves providesdither so that there is substan tially no static friction to be overcomein the operation of the valves.

The important advantage of providing dither for the pilot valves 74 and76 is brought out clearly by a comparison of FIGS. 9 and 10. FIG. 9shows a curve 2241 which plots flow of fluid past an open pilot valveagainst the voltage applied to the solenoid that operates the valve. Thevoltage used for FlG. 9 was direct current voltage without pulses andwithout dither of the valves. lt is apparent that when the valve isopened to increase the rate of flow there is much less flow for a givenvoltage on the solenoid as compared with the condition where the valveis closed. The difference in flow rate at voltage Y-ll is represented bythe distance from 74-1 to X-2 on the chart, and it is of substantialmagnitude.

In FIG. a curve 226 corresponds to the curve 224 of FIG. 9, but thevoltage applied to the valve-operating solenoid was a pulsing powersupplied as shown in FIG. 8 with resulting dither of the valve. Thedecreasing flow portion of the curve of FIG. 10 is close to theincreasing flow portion and at some points the two portions of the curveintersect indicating identical fluid flow for a given solenoid voltageregardless of whether the flow is increasing or decreasing, that is,whether the valve is opening or closing. This makes the rate of changesubstantially uniform for a given position of the control handles and isespecially important when automatic control is substituted for manual.

The preferred embodiment of the invention has been illustrated anddescribed and the invention is described in the appended claims.

What is claimed is:

l. The combination with a roll mill having rolls forming a pass throughwhich a metal workpiece travels and having pressure operated motor meansfor moving one roll with respect to the other roll of the roll pass tochange the pressure of the roll on the workpiece, of means for supplyingworking fluid to said motor means including a pressure regulator havingan inlet for receiving high pressure working fluid from a working fluidsource at fixed or variable pressure and an outlet connected with themotor means, valve means in the pressure regulator commanding flow fromthe inlet to the outlet, a valve chamber in the pressure regulatorsupplied with pressure from the outlet and from the downstream side ofthe valve means, an actuator for the valve means exposed to the chamberpressure for closing the valve means when the chamber pressure reaches apredetermined pressure, and adjustable means movable into differentpositions to change the downstream pressure at which the actuatoroperates the valve means.

2. The combination described in claim 1 characterized by the pressureregulator including a loaded relief valve through which working fluidescapes from said valve chamber when the pressure of the working fluidat the outlet exceeds a predetermined value.

3. The combination described in claim 2 characterized by the workingfluid being a liquid and the motor means including twocylinder-and-piston hydraulic motors, a different one of which isconnected with each end of the roll, a sump from which working fluid issupplied to the pressure regulator and to which the working fluid flowsfrom said relief valve, and a pump that delivers liquid from the sump tothe inlet of the pressure regulator.

4. A pump system for correcting errors in the thickness of metal beingrolled in a rolling mill including in combination pressure devices forchanging the pressure of rolling mill rolls on the metal, a transducerfor detecting errors in the thickness of the metal as it comes from theroll pass, separate pressure regulators that supply working fluid toeach of the pressure devices, each of the regulators having an inlet forreceiving high pressure working fluid from a working fluid source atfixed or variable pressure and an outlet connected with the pressuredevices, valve means in the pressure regulator commanding flow from theinlet to the outlet, a valve chamber in the pressure regulator suppliedwith pressure from the outlet and from the downstream side of the valvemeans, an actuator for the valve means exposed to the chamber pressurefor closing the valve means when the chamber pressure reaches apredetermined maximum pressure, each of the actuators including amovable wall exposed on one side to the pressure of the valve chamber,each of the regulators also having a loading chamber on the other sideof the movable wall, other valve means for supplying fluid to andexhausting fluid from the loading chambers of the regulators, anddevices for operating said other valve means in accordance with errorsdetected by the transducer.

5. The system described in claim 4 characterized by the pressure devicesbeing hydraulic motors on different sides of the rolling mill, therebeing a plurality of transducers at different locations across the widthof the metal being rolled, there being different valve means for eachpressure regulator for supplying fluid to and exhausting fluid from theloading chambers of the pressure regulators, and the devices foroperating said valve means including a different manually actuatedelement for each valve means for selectively operating the valve meansin accordance with the errors detected by the transducer.

6. A pump for correcting errors in the thickness of metal being rolledin a rolling mill including in combination pressure devices for changingthe pressure of rolling mill rolls on the metal, a transducer fordetecting errors in the thickness of the metal as it comes from the rollpass, separate pressure regulators that supply working fluid to each ofthe pressure devices, each of the regulators having a loading chamber,valve means for supplying fluid to the loading chambers of theregulators,

and devices for operating said valve means in accordance with errorsdetected by the transducer, characterized by the pressure devices beinghydraulic motors on different sides of the rolling mill, there being aplurality of transducers at different locations across the width of themetal being rolled, there being different valve means for supplyingfluid to the loading chambers of the pressure regulators, and thedevices for operating said valve means including a different manuallyactuated element for each valve means for selectively operating thevalve means in accordance with the errors detected by the transducer,and further characterized by the rolling mill having long rolls forrolling metal sheets, and the rolling mill being a four high mill withcrowned work rolls and a backup roll behind each of the work rolls, thevalve means that supply fluid to the loading chambers of the pressureregulators also including means for venting the loading chambers toreduce the loading on the pressure regulators, the loading chambersbeing loaded with liquid and having two movable walls, one of which hasspring means on the side opposite the loading chamber which arecompressed by displacement of the movable wall to increase the pressureof the liquid in the loading chamber, and the other of which connectswith a main valve of the regulator for controlling the flow of liquidthrough the pressure regulator.

7. The system described in claim 6 characterized by the connectionbetween one of the movable walls of the loading chamber and the mainvalve of the regulator being made in two parts in end-to-end abutmentfor displacing the main valve, a relief valve on one of said parts, aseat for the relief valve on the other of said parts, the relief valvebeing opened by continued movement of its connected movable wall of theloading chamber after the main valve of the pressure regulator has movedinto closed position, and a pressure chamber exposed to the outletpressure of the regulator and located on the side of said other wall,which side is the one away from the loading chamber of the regulator.

1. The combination with a roll mill having rolls forming a pass throughwhich a metal workpiece travels and having pressure operated motor meansfor moving one roll with respect to the other roll of the roll pass tochange the pressure of the roll on the workpiece, of means for supplyingworking fluid to said motor means including a pressure regulator havingan inlet for receiving high pressure working fluid from a working fluidsource at fixed or variable pressure and an outlet connected with themotor means, valve means in the pressure regulator commanding flow fromthe inlet to the outlet, a valve chamber in the pressure regulatorsupplied with pressure from the outlet and from the downstream side ofthe valve means, an actuator for the valve means exposed to the chamberpressure for closing the Valve means when the chamber pressure reaches apredetermined pressure, and adjustable means movable into differentpositions to change the downstream pressure at which the actuatoroperates the valve means.
 2. The combination described in claim 1characterized by the pressure regulator including a loaded relief valvethrough which working fluid escapes from said valve chamber when thepressure of the working fluid at the outlet exceeds a predeterminedvalue.
 3. The combination described in claim 2 characterized by theworking fluid being a liquid and the motor means including twocylinder-and-piston hydraulic motors, a different one of which isconnected with each end of the roll, a sump from which working fluid issupplied to the pressure regulator and to which the working fluid flowsfrom said relief valve, and a pump that delivers liquid from the sump tothe inlet of the pressure regulator.
 4. A pump system for correctingerrors in the thickness of metal being rolled in a rolling millincluding in combination pressure devices for changing the pressure ofrolling mill rolls on the metal, a transducer for detecting errors inthe thickness of the metal as it comes from the roll pass, separatepressure regulators that supply working fluid to each of the pressuredevices, each of the regulators having an inlet for receiving highpressure working fluid from a working fluid source at fixed or variablepressure and an outlet connected with the pressure devices, valve meansin the pressure regulator commanding flow from the inlet to the outlet,a valve chamber in the pressure regulator supplied with pressure fromthe outlet and from the downstream side of the valve means, an actuatorfor the valve means exposed to the chamber pressure for closing thevalve means when the chamber pressure reaches a predetermined maximumpressure, each of the actuators including a movable wall exposed on oneside to the pressure of the valve chamber, each of the regulators alsohaving a loading chamber on the other side of the movable wall, othervalve means for supplying fluid to and exhausting fluid from the loadingchambers of the regulators, and devices for operating said other valvemeans in accordance with errors detected by the transducer.
 5. Thesystem described in claim 4 characterized by the pressure devices beinghydraulic motors on different sides of the rolling mill, there being aplurality of transducers at different locations across the width of themetal being rolled, there being different valve means for each pressureregulator for supplying fluid to and exhausting fluid from the loadingchambers of the pressure regulators, and the devices for operating saidvalve means including a different manually actuated element for eachvalve means for selectively operating the valve means in accordance withthe errors detected by the transducer.
 6. A pump for correcting errorsin the thickness of metal being rolled in a rolling mill including incombination pressure devices for changing the pressure of rolling millrolls on the metal, a transducer for detecting errors in the thicknessof the metal as it comes from the roll pass, separate pressureregulators that supply working fluid to each of the pressure devices,each of the regulators having a loading chamber, valve means forsupplying fluid to the loading chambers of the regulators, and devicesfor operating said valve means in accordance with errors detected by thetransducer, characterized by the pressure devices being hydraulic motorson different sides of the rolling mill, there being a plurality oftransducers at different locations across the width of the metal beingrolled, there being different valve means for supplying fluid to theloading chambers of the pressure regulators, and the devices foroperating said valve means including a different manually actuatedelement for each valve means for selectively operating the valve meansin accordance with the errors detected by the transducer, and furthercharacterized By the rolling mill having long rolls for rolling metalsheets, and the rolling mill being a four high mill with crowned workrolls and a back-up roll behind each of the work rolls, the valve meansthat supply fluid to the loading chambers of the pressure regulatorsalso including means for venting the loading chambers to reduce theloading on the pressure regulators, the loading chambers being loadedwith liquid and having two movable walls, one of which has spring meanson the side opposite the loading chamber which are compressed bydisplacement of the movable wall to increase the pressure of the liquidin the loading chamber, and the other of which connects with a mainvalve of the regulator for controlling the flow of liquid through thepressure regulator.
 7. The system described in claim 6 characterized bythe connection between one of the movable walls of the loading chamberand the main valve of the regulator being made in two parts inend-to-end abutment for displacing the main valve, a relief valve on oneof said parts, a seat for the relief valve on the other of said parts,the relief valve being opened by continued movement of its connectedmovable wall of the loading chamber after the main valve of the pressureregulator has moved into closed position, and a pressure chamber exposedto the outlet pressure of the regulator and located on the side of saidother wall, which side is the one away from the loading chamber of theregulator.